Fetal abnormalities » Urinary tract

Urethral obstruction

Prevalence:

1 in 1,500 males

Ultrasound diagnosis:

Urethral obstruction can be caused by urethral agenesis, persistence of the cloaca, urethral stricture or posterior urethral valves.

With posterior urethral valves, there is usually incomplete or intermittent obstruction of the urethra, resulting in an enlarged and hypertrophied bladder with varying degrees of hydroureters, hydronephrosis, a spectrum of renal dysplasia (echogenic renal parenchyma with peripherally placed cysts), oligohydramnios and pulmonary hypoplasia.

In some cases, there is associated urinary ascites from rupture of the bladder.

Reduced amount of the amniotic fluid >17 weeks’ gestation.

In the first trimester the condition presents as megacystis (longitudinal bladder diameter of ≥7 mm). If the bladder diameter is 7-15 mm there is spontaneous resolution of the megacystis in about 90% of cases. If the bladder diameter is ≥15 mm the condition is invariably associated with progressive obstructive uropathy leading to hydronephrosis and dysplastic kidneys.

Associated abnormalities:

Chromosomal defects, mainly trisomies 21, 18 or 13, are found in about 10% of cases.

Other defects, mainly cardiac and gastrointestinal are found in up to 40% of cases.

Investigations:

Detailed ultrasound examination.

Amniocentesis for karyotyping or analysis of cfDNA from maternal blood.

Fetal therapy:

Decompression of the urinary tract has been achieved by ultrasound-guided insertion of suprapubic vesico-amniotic catheters and cystoscopic ablation of urethral valves. Although these techniques demonstrated the feasibility of intrauterine surgery, they did not provide conclusive evidence that such intervention improves renal or pulmonary function.

Follow up:

If pregnancy continues, ultrasound scans every 4 weeks to monitor the evolution of the condition and assess amniotic fluid volume.

Delivery:

Place: hospital with neonatal intensive care and pediatric surgery.

Time: 38 weeks.

Method: induction of labor aiming for vaginal delivery.

Prognosis:

Severe: high perinatal mortality due to pulmonary hypoplasia secondary to severe oligohydramnios. Even in those that survive, about 30% develop renal failure necessitating dialysis and / or transplantation before the age of 5 years.

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